Gordon M. Goldstein is an adjunct Senior Fellow at the Council on Foreign Relations and the author of “Lessons in Disaster: McGeorge Bundy and the Path to War in Vietnam.”

Soon after the collapse of Saigon during the grinding conclusion of the Vietnam War, “each officer assigned to the United States Naval War College for the 1975-76 academic year received a puzzling package in the mail,” recalls Yale University professor John Lewis Gaddis. “Inside was a thick paperback with instructions to read it — all of it — before arrival in Newport.” The book was Thucydides’ “The Peloponnesian War,” a history of the 5th-century BC geopolitical and military contest between Athens and Sparta, which through the centuries has remained an essential work of international relations theory. Adm. Stansfield Turner, a future director of the CIA, “was determined that we would cover Vietnam . . . even if we had to get there by a 2,500-year detour,” explains Gaddis, who was recruited by Turner to teach a seminar in the academic discipline known as grand strategy. “The Peloponnesian War” served as a prism for weeks of intense discussion about America’s disastrous entrapment in Vietnam. “We were doing post-traumatic stress therapy before it had a name,” Gaddis writes. “Thucydides trained us.”

Decades later Gaddis continues to lecture on the theme of grand strategy, which he defines as the “alignment of potentially unlimited aspirations with necessarily limited capabilities” of states and their leaders. One of the world’s preeminent diplomatic historians, Gaddis has collected his reflections and musings in a remarkably erudite volume titled “On Grand Strategy,” which by the author’s own admission is an “informal, impressionistic, and wholly idiosyncratic” treatment of strategy and world history.

Gaddis renders nuanced verdicts on an eclectic cohort of thinkers, writers, monarchs and conquerers, including Machiavelli, Carl von Clausewitz, Cicero, the Roman Empire of Mark Antony and Caius Julius Caesar Octavianus, Tolstoy, Shakespeare, the Oxford political philosopher Isaiah Berlin, and the Chinese military strategist Sun Tzu, whom the author marginalizes with sly derision for his imprecise generalizations. Even the novelist F. Scott Fitzgerald makes a cameo appearance. Throughout Gaddis is cheerfully candid in clarifying his purpose. Winner of the Pulitzer Prize for his biography of George Kennan, the intellectual architect of the post-World War II doctrine of containment, Gaddis conspicuously omits this historical era although it is intrinsic to his theme. “Some readers may worry that I’ve forgotten the Cold War,” he acknowledges in an endnote. “Not at all — it’s just that I have said enough about that subject.” Gaddis has indisputably earned the right to plow different fields of historical inquiry, which he does in “On Grand Strategy” with self-evident glee and peripatetic curiosity.

He declares that Augustine’s “City of God” is “a loose, baggy literary leviathan — a Moby Dick of theology — in which cycles and epicycles, angels and demons, myths and histories jostle one another in no particular order. Making it a manual for strategy, much less for salvation, is devilishly difficult.” Abraham Lincoln, in contrast, captures the ideal of deep strategic insight fused with moral resolve and determination. “He read voraciously, remembered pragmatically, and applied lessons ingeniously.” Lincoln realized that civil war, as bloody and awful as it would be, “might also permit the American state, tainted by slavery, to save its soul.”

Queen Elizabeth’s challenge and ultimate success in the 16th century to consolidate her reign provides further instruction. Gaddis portrays her as a resourceful, agile strategist: “Relishing opposites, the queen was a constant only in her patriotism, her insistence on keeping ends within means, and her determination — a requirement for pivoting — never to be pinned down.” Elizabeth was utilitarian and ruthless. “In 1573 she made Sir Francis Walsingham her secretary of state, with orders to do whatever necessary . . . to guard queen and country.” Elizabeth empowered Walsingham to employ espionage and covert action to protect the throne. “Using bribery, theft, entrapment, blackmail, and torture, he built a network of informants stretching across Europe.”

While Elizabeth was cunning and disciplined, Napoleon was brilliant but compromised by grandiosity. Hoping to shock Czar Alexander into a peace settlement, the French emperor invaded Moscow in June 1812, finding it abandoned and accomplishing nothing of strategic value. “The greatest military genius since Julius Caesar,” Gaddis notes sardonically, “assumed the attributes of a dog who’d chased a car and caught it: what do you do next?” The 600,000 French soldiers who stormed Russia’s capital were doomed. By December, Napoleon’s army was reduced to 90,000. “This rate of attrition,” Gaddis observes, “couldn’t help but revive a question asked of the Persians in Greece, the Athenians in Sicily, the Romans in the Teutoburg forest, the Spanish in the English Channel, and the British in America: what were they thinking?” Gaddis defines a historical lesson to be extracted from such disparate disasters. “Overstretch — the enfeeblement that comes with confusing ends and means — allows enemies to apply leverage: small maneuvers that have big consequences.”

These examples of misapplied strategic ambition and miscalculated military intervention are the most illuminating in the author’s elegantly composed study. They bind ancient and modern history to provide practical guidance to the contemporary strategist.

Thucydides, regarded as the original progenitor of the school of political realism, famously observed that “the strong do what they can and the weak suffer what they must.” But as his history teaches us, the strong are not necessarily wise. As Gaddis recounts, Megara was a “molehill” at the northeastern end of the Corinthian isthmus whose citizens “had long feuded with the Athenians, while posing no military threat to the larger city.” Athens nonetheless imposed “an economic embargo designed to discourage future defections by nonmilitary means.” The Spartans made its revocation one of their conditions for avoiding war. “Instead Pericles,” the Athenian leader, philosopher and orator, “convinced himself that he couldn’t concede a molehill — the Megarian decree — without a mountainous loss of credibility.” Athens pursued a path to war that eventually would result in the loss of its empire.

Gaddis is fascinated by the risks statesmen have embraced throughout history by fixating on perceptions of credibility. One example he does not cite that nonetheless advances his analysis can be found in the struggle of McGeorge Bundy, national security adviser during the Vietnam War. On March 21, 1965, less than two weeks after the first 3,500 U.S. Marines waded ashore in Danang, Bundy recorded his private reflections on a yellow legal pad, trying to grasp the essence of a momentous commitment to a likely unwinnable war. The “cardinal” principle of the Vietnamese intervention, Bundy wrote, was for the United States “not to be a paper tiger. Not to have it thought that when we commit ourselves we really mean no major risk.” For Bundy the perception of credibility outweighed even the requirement of victory. “For if we visibly do enough, whatever that may be, any failure will be . . . beyond our control.” Even a failed intervention in Vietnam, Bundy reasoned, would be better than no intervention at all. “Questions: in terms of U.S. politics which is better: to ‘lose’ now or to ‘lose’ after committing 100,000 men? Tentative answer: the latter.”

Perhaps if Bundy had studied Thucydides — and his brilliant interpreter Gaddis — that judgment would have been decided differently.

On Grand Strategy

By John Lewis Gaddis

Penguin Press. 368 pp. $26